One engine or two?

[MapisM]

maybe MapisM might wish to defend his comments??

Naah, there's nothing wrong in what the other posters said.
In any MoBo meant as a weekend toy for coastal cruising (which is what most pleasure MoBos are designed to be), it's very nice to have two blocks. If the electronic gizmo in one of them goes nuts, there's the other one. And of course there are much more chances to grab a net with two exposed shafts/legs/props/rudders, compared to an extremely protected single screw spinning behind a huge keel. So it's good to have two of each. And so forth.

See, maybe I misunderstood what you said in your OP, because by "offshore cruiser" I assumed you were interested in long range boats - hence my reply along the lines of ocean going vessels. Which are in another league compared to the average pleasure boat. A league where the engine reliability is obviously paramount, but the same is true also for economy, range, accessibility, onboard systems, fuel filtration with separate day tanks, and so on.
In these boats, most builders and owners seem to agree that the single is the way to go, at least up to a certain size, let's say 65 feet or so. Above that, there are other reasons which make twins a sensible alternative.

And at the end of the day, it's also down to personal preferences.
'Fiuaskme, I'd rather be at 500Nm from the nearest coast on a steel boat as a Molokai Strait and the likes, spinning a single, commercial rated engine, than on a Pershing 115 with 2 hi-performance diesels and 1 gas turbine.

PS: coming to think of it, I'm not even sure that the Pershing could make it, to that 500Nm distant coast...

 

[Piers]

The one or two argument will run for years more!

For me, I used to be a speed freak, but now (maybe because of age?) I prefer displacement speed cruising and enjoying the passage making. The family prefers it as well, being able to watch movies, cook meals, take turns driving, clean teak decks, polish the stainless, do homework, etc.

A single would be my preference, but Fleming doesn't make their boats with singles.

To me, a single has more space around it which in turn would have better access to those awkward parts which would encourage better servicing. Cost would be less, the prop would be better protected by the keel, etc, etc.

I would also instal a centrifugal fuel polisher (using Alfa Laval kit) and configure a polished fuel day tank.

Many trawler yachts like the Fleming in the States are single engine, with some having a 'get me home wing' engine which in some circumstances may be a take-off from a gen set.

The previous editor of Passage Maker (the MBM/MBY equivalent in the States) always preferred single engine installations, and often wrote reams on why. His surveys showed an equal split between the two camps.

 

[gjgm]

it somewhat depends what you mean by offshore cruiser. Most leisure planing boats reach a size where you tend to need two engines to get it up and humming !
Maybe thats about 30/34 ft. But if you are happy going a bit slower, then some larger leisure boats will manage on one (Nimbus, I think).
Some argue twice the props etc means twice as likely to get something tangled !
For me, if its going to be more highly stressed, higher output,higher speed.. its got to be two. But I d be happy to have one engine if we re talking tops at lowish 20knots.

 

[AndieMac]

Just spent the afternoon aboard a Nordhaven 46 after she had come in from an 1100 mile open ocean passage. She certainly had all the boxes ticked by her owners when new and a lot more besides in the following years of cruising.
A most impressive vessel, with equally impressive owners.

There is no problems heading to sea with her single engine 135 H.P., and as Piers mentioned, polished fuel through a day tank, with every conceivable back up and safety system known to man-kind.

These vessels of course, are designed specifically to cover great distances and remain self sufficient for long periods of time in remote locations, for the hardy souled few, who are up to the task.......and of course, who can afford them.

They certainly have my vote.

 

[MapisM]

Just spent the afternoon aboard a Nordhaven 46 after she had come in from an 1100 mile open ocean passage. She certainly had all the boxes ticked by her owners when new and a lot more besides in the following years of cruising.
A most impressive vessel, with equally impressive owners.

Blimey, you're making me envious now.
I followed the Flanders voyage on the web, they surely are impressive people. If you'll meet them again, tell them that there's a fan of theirs in Italy with a good bottle of wine ready, whenever they would be around here.

 

[Deleted User YDKXO]

Just spent the afternoon aboard a Nordhaven 46 after she had come in from an 1100 mile open ocean passage. She certainly had all the boxes ticked by her owners when new and a lot more besides in the following years of cruising.
A most impressive vessel, with equally impressive owners.

There is no problems heading to sea with her single engine 135 H.P., and as Piers mentioned, polished fuel through a day tank, with every conceivable back up and safety system known to man-kind.

These vessels of course, are designed specifically to cover great distances and remain self sufficient for long periods of time in remote locations, for the hardy souled few, who are up to the task.......and of course, who can afford them.

They certainly have my vote.

Lovely boat but it costs €1m and has a run for ever Lugger or similar engine in it. The OP hasn't indicated what size and price level of boat he's considering but I doubt it's a Nordhavn. If he's talking an average 30 footer with single engine, then the boat will no doubt have a rev it's nuts off Volvo engine in it and definitely no fuel polishing system or day tank. I agree entirely that if you throw enough money at a single engined boat and fit a wing engine, a fuel polishing system, a day tank, double fuel filtering system etc etc you can make it pretty failsafe but most single engined boats are not like that.
Anyway, virtually every single engined bluewater motor boat on the market has a wing engine or additional hydraulically driven prop. If single engined boats can be made so incredibly reliable, why do they need a back up engine and isn't a single engined boat with a wing engine a twin engined boat anyway?

 

[MapisM]

virtually every single engined bluewater motor boat on the market has a wing engine or additional hydraulically driven prop. If single engined boats can be made so incredibly reliable, why do they need a back up engine and isn't a single engined boat with a wing engine a twin engined boat anyway?

Mike, the answers to your questions are "they don't" and "no", respectively.
They don't really "need" a wing engine, it's just that pleasure boaters - even the most adventurous one - after all are at sea just for pleasure, and they prefer (and can afford) any safety net they can get. I've seen for instance a 100T 60' steel trawler, with a single 380hp engine (same block good for 800hp on its pleasure version) with a sailboat wing engine, 40hp or so (btw, I've never seen an "additional hydraulically driven prop", wazzat?). Anyway, you know what? I'd rather deploy a sea anchor than rely on that wing engine, in any kind of serious sea! Besides, most of those who are at sea for a living don't have a wing engine, simply because it would be a useless additional cost.

And re. being a single+wing the same as a twin, not at all!
Singles still have the centered, extremely protected prop & rudder. They still enjoy the better efficiency, economy and range. Better e/r accessibility, less maintenance, etc.

100% agreed on the planing 30 footer thing, if that's what the OP had in mind (which is not what I understood, but that's me).
Apropos - in reply to those who pointed out that SAR boats have twins: that's due to the operational requirement they're designed to cope with, among which speed has its place. Not to safety reasons.

 

[Deleted User YDKXO]

Mike, the answers to your questions are "they don't" and "no", respectively.
They don't really "need" a wing engine, it's just that pleasure boaters - even the most adventurous one - after all are at sea just for pleasure, and they prefer (and can afford) any safety net they can get. I've seen for instance a 100T 60' steel trawler, with a single 380hp engine (same block good for 800hp on its pleasure version) with a sailboat wing engine, 40hp or so (btw, I've never seen an "additional hydraulically driven prop", wazzat?). Anyway, you know what? I'd rather deploy a sea anchor than rely on that wing engine, in any kind of serious sea! Besides, most of those who are at sea for a living don't have a wing engine, simply because it would be a useless additional cost.

And re. being a single+wing the same as a twin, not at all!
Singles still have the centered, extremely protected prop & rudder. They still enjoy the better efficiency, economy and range. Better e/r accessibility, less maintenance, etc.

100% agreed on the planing 30 footer thing, if that's what the OP had in mind (which is not what I understood, but that's me).
Apropos - in reply to those who pointed out that SAR boats have twins: that's due to the operational requirement they're designed to cope with, among which speed has its place. Not to safety reasons.

Mario, have to agree to disagree on this one. A single + wing is of course not the same as a twin in terms of propulsion but in terms of having a back up engine in case one fails, what's the difference? In principle they are the same. If one engine fails you have the other so a single + wing is not a single engine system. Of course I know that wing engines are much smaller than the main engine but they have to be powerful enough to drive the boat otherwise there is no point in fitting them. With regard to hydraulic drive, I think some single engined boats do not have a separate wing engine but rely on a hydraulic PTO on the generator which drives a hydraulic motor attached to the wing prop. Seems like a sensible solution to me if you don't have the space or want to spend the money on a separate wing engine which does nothing for 99.999% of the time. However the major bluewater mobo builders eg Nordhavn, Kadey, Selene all offer wing engine options on their single engined models so there must be a need/demand for them

 

[nedmin]

Talking about wing engines,,Has anyone fitted a Jetski unit to do the job? THought about it a few times,if I was young and daft it would be a good project.

 

[Nealo]

I can see we're reaching that "agree to differ" point.

Just to clarify, I was a bit vague in the phrasing of the question really because I'm in the early stages of the RYA syllabus but have already come across some quite forceful opinions on this issue along the lines of "I would never go anywhere at sea with only one engine". And having been exposed to the addictive qualities of twin screw boats, it seemed to be a no choice situation.

One factor that seems to crop up in all the communications I've had regarding engines is the dirty fuel issue. Is this solely to do with the quality of the supply or is there some other reason why marine engines are prone to it?

 

[AndieMac]

Blimey, you're making me envious now.
I followed the Flanders voyage on the web, they surely are impressive people. If you'll meet them again, tell them that there's a fan of theirs in Italy with a good bottle of wine ready, whenever they would be around here.

I went down to check out the Flanders boat yesterday after reading this thread regarding the single engine with a wing motor. They have a Yanmar 27 H.P. on a V drive, to a folding prop. The little motor is mounted well aft (thus the V drive) but sits pretty close to the centre-line of the boat, about 2 feet to port, from the main engines' prop shaft.
Scott said they had only used it once, in Italy, when they backed over the dinghys painter line. It will push the boat at 3.5 knots in flat water with no tide.

They have this great setup for the sea anchor/parachute.
Leading from a huge eye fitting on the stem, just above the waterline, directly up to the bow roller is this substantial kevlar line, tweaked tight. The 20mm line runs back aft, via the outside of the bow rail, attached by cable ties, to the portuguese bridge deck where 600 feet of more line and the parachute bag and bouys are sitting, ready to be thrown into the sea, if necessary.

He explains these systems on his blog on the Norhaven site, but it has been fantastic to see the setup for real.

You have to remember, down here at the 'end of the earth' we don't get that many visitors, which appears to be the main attraction for these cruising folk.

 

[MapisM]

I went down to check out the Flanders boat yesterday after reading this thread regarding the single engine with a wing motor. They have a Yanmar 27 H.P. on a V drive, to a folding prop. The little motor is mounted well aft (thus the V drive) but sits pretty close to the centre-line of the boat, about 2 feet to port, from the main engines' prop shaft.
Scott said they had only used it once, in Italy, when they backed over the dinghys painter line. It will push the boat at 3.5 knots in flat water with no tide.

They have this great setup for the sea anchor/parachute.
Leading from a huge eye fitting on the stem, just above the waterline, directly up to the bow roller is this substantial kevlar line, tweaked tight. The 20mm line runs back aft, via the outside of the bow rail, attached by cable ties, to the portuguese bridge deck where 600 feet of more line and the parachute bag and bouys are sitting, ready to be thrown into the sea, if necessary.

Very interesting. Reminds me of the 60’ steel trawler I mentioned before. The first owner built her with the aim of cruising Antarctica, and rigged that boat from the start for sea anchor deployment, with a huge winch inside the portuguese bridge, an extremely strong and long steel cable and a specifically built fairlead, near the two anchor rollers. And he didn’t wait a lot to test it, either: during the maiden voyage in northern Atlantic, after deliberately waiting for nasty sea conditions before crossing, together with his wife and children…
Apropos, that boat had another peculiar arrangement for the wing engine, to make it in a sense even safer than two mains: it was installed in a utility room, not in the engine room. And these compartments were separated by steel bulkheads and a water+fireproof door, with cut-off valves on the diesel lines. Therefore, even in the catastrophic event of a major fire or flooding in the e/r, the wing still had good chances to remain usable. That’s practically impossible to arrange, with two mains.

 

[MapisM]

Mario, have to agree to disagree on this one. A single + wing is of course not the same as a twin in terms of propulsion but in terms of having a back up engine in case one fails, what's the difference? In principle they are the same. If one engine fails you have the other so a single + wing is not a single engine system. Of course I know that wing engines are much smaller than the main engine but they have to be powerful enough to drive the boat otherwise there is no point in fitting them. With regard to hydraulic drive, I think some single engined boats do not have a separate wing engine but rely on a hydraulic PTO on the generator which drives a hydraulic motor attached to the wing prop. Seems like a sensible solution to me if you don't have the space or want to spend the money on a separate wing engine which does nothing for 99.999% of the time. However the major bluewater mobo builders eg Nordhavn, Kadey, Selene all offer wing engine options on their single engined models so there must be a need/demand for them

Well, I can't see any major disagreement actually.
I did say that the demand is there, on pleasure crafts. "Need" is imho just too strong: would it be a real need, wing engines would be the norm also on working boats, whilst they aren’t.
Re. your question "isn't a single+wing a twin engined boat anyway?", you seemed to imply (or that's what I understood anyway) that if so, why not just fit two mains? Hence my reply.
But of course I agree on the principle as such, a single+wing is not a “pure” single.

Re. the genset+ pump attached to a PTO+hydraulic motor, yup, now I see what you mean.
But I've never heard of such arrangement. Surely it must be very rare.
There are at least a couple of good reasons which spring to my mind:
1) the genny as a get home system is a good idea only in theory, because on the type of boats we're talking about (up to 20m or so: above that, as I said previously, twin mains are more common), you end up having either a too big, noisy, underutilized and prone to glazing genny, or too small a get home. Take the Flanders' boat for instance: they should use a 40kw genset to get approximately the same propshaft power of their dedicated wing engine. Which is a nonsense: as I recall from their blog, they have a 12kw onboard, and even considered to donwize it, at some stage.
Btw, contrarily to what common sense may suggest, even the dedicated wing actually isn't "powerful enough to drive the boat". I mean, not when it would be mostly appreciated, that is in very heavy seas. The storm tactics, if the main gets disabled in these conditions, involve invariably the use of the wing just to deploy the sea anchor, stabilize the boat and deal with the main engine problem. For those who have an idea of what the deployment of a sea anchor in awfully strong winds practically means, this goes a long way to explain how much even those who fit a wing on their boat actually trust the main to do its job, to start with.
2) if anyone would really want to use the genny as a get home, it's simpler to use directly an electric motor, rather than go through the hydraulic conversion. In fact, I've actually seen one boat rigged in this way, though it remains a noticeable exception. And as I was told, it was just good enough to move the boat at less than 3kts...

 

[Nick_H]

The distinction between a twin engined boat and a single with wing engine is semantics IMO, in the reliability/get me home debate. Most (all?) twin engined planing boats can't plane on one engine, so the benefit of two is that you can get home at displacement speed if one engine fails. In that respect at least, the wing engine achieves the same purpose, albeit at a slower speed.

As others have said the reference to commercial craft is not relevant, as few pleasure boat owners are fully trained mechanics themselves, or have one as crew, and even if they were/did, they don't have the facilities on board to effect major repairs.

I guess the Flanders are happy they spec'ed a second drive system, as they had to use it?

 

[late-night-lochin]

When I mentioned "commercial" boats, I was thinking of things like sub 40ft commercial fishing boats and charter fishing and diving boats, typcially things like Aquastars and Offshore 105s etc. Most of these are semi displacement craft and and generally use high performannce diesels up to 500 or more HP.

These boats are generally owned and financed by the skipper rather than a govenment department or an institution. He will have done his sums regarding cost vs reliability when he bought the boat as he knows that if the boat breaks down, he will lose money and probably his reputation. This type of craft can also do more hours in a week than many leisure boats do in a season.

As we know there is a lot of "tradidion" in boating, some of it justified some of it more like "old wives tales". If we consider a sports boat from the 1960s e.g. a Fairey Huntsman, they were twin engined but thats because, in those days, a 200HP (relatively lightweight as opposed to low revving Gardner type) was a monster but the Fairy Huntsman needed more than 200HP so they put two in, fine!

However diesel technology has moved on a long way since then (as have petrol engines) and those "tractor engines" are now powering winning cars in the Le Mans 24 Hour race dammit.

I would sugest that a single 400HP diesel fitted to modern 30ft sports boat would have many advantages over a pair of 200 HP engines. It would be faster because of less underwater drag and less weight etc. The single engine would be mounted deeper down on the centre line of the hull so the boat should be more stable and handle better. The single engine would take up considerable less room so would improve accommodation or deck space. Access would potentially be far easier which could reduce maintenance costs and if everything is readilly accessible it would increase the chances of it being maintained correctly. The boat would burn less fuel and should cost less to buy.

Obviously, if a boat was a lot bigger and needed 1000HP, the argument wouldn't stack up but the point that I'm trying to make is that size where twins becomes desirable and viable has changed drastically over the years.